Pneumatically operated fastener driving machine



March 19, 1963 J. E. GOLDRING 3,081,740

PNEUMATICALLY OPERATED FASTENER DRIVING MACHINE Filed Nov. 14, 1955 3 sheetsrsheet 1 JOHN E. GOLDRING March 19, 1963 J. E. GOLDRING 3,081,740

PNEUMATICALLY OPERATED FASTENER DRIVING MACHINE Filed Nov. 14, 1955 5 Sheets-Sheet 2 fVVEHZZUF Jo/4- E. Gown we March 19, 1963 J. E. GOLDRING PNEUMATICALLY OPERATED FASTENER DRIVING MACHINE 3 Sheets-Sheet 15 Filed Nov. 14, 1955 t i i 3 dbl 740 a a i z Q Fatei'ited Mar. 19, 1953 matically operated fastener driving machines for eco- 3,t)8l,74 nomical mass production, ease and convenience in servic.

FNEUMATiCALLY GFEEATED FASTENER DRIVENG MACHENE lohn E. Goldring, f-ian Leandra, Calif, assignor, by mesne assignments, to Modernair Corporation, Bryan, Ghio, a corporation of @hio Filed Nov. 14, $55, Sen No. 546,5ti'9 Elain -s. (6i. 123-21) The present invention relates to improvements in pres sure fluid operated fastener driving machines.

The use of pressure fluid such as compressed air, CO or other gases for motivating fastener driving devices has received considerable attention in view of the increasing use in industry and various trades of machines for driving various types of nail or pin or staple fasteners in securing together members that hereto-fore may have been manually nailed together. By motivating the fastener driving machines pneumatically (that is, by a compressible pressure fluid) reduction in weight of the mechanism, greater and more positive driving force, as well as substantial reduction in strain and fatigue upon the operator can be attained.

However, the harnessing of the fluid force to the specific function of motivating a fastener driving device has presented certain definite problems among which the most serious problem has been that of objectionable recoil on the order of that unleashed as a result of the explosive forces generated in firing a weapon type of gun. This has been caused in pneumatic fastener drivers apparently by reason of the similar reaction in the chamber space behind the piston as occurs in the chamber space behind the projectile or bullet in a firearm where the expanding gases of the explosive charge react toward the head of the chamber opposite the projectile, thereby tending to move the gun away from the projectile which is moved by the expanding gases toward the muzzle of the gun where the gases can exhaust. The same principle operates in a jet type fluid motor where the pressure created against the unyielding head of the chamber in which the expanding gases are confined creates a thrust in the direction of the head. In a pneumatic fastener driving gun such reaction of the compressed gas in the piston chamber or cylinder is toward the head end thereof and this is reflected in a recoil or hopping action of the machine, and more especially in those machines where the compressed gas is introduced into the head space above the piston without any initial restraint upon stroking movement of the piston as the pressure fluid is suddenly released under driving pressure into the cylinder.

It is accordingly an important object of the present invention to provide a pneumatically operated fastener driving device in which there is substantially complete freedom from fluid pressure recoil incident to the driving stroke of the fastener driver.

Another object of the invention is to provide pneumatically actuated fastener driving means in which the transition from at rest or non-operating to the full effective fluid pressure actuated driving stroke is accomplished smoothly and without recoil reaction.

A further object of the invention is to provide a fastener driving mechanism in which greatly increased efficiency in the use of compressed gas such as air is attained both with respect to the volume of gas used in a driving stroke and in the positive application of the energy derived from the gas actually used.

Still another object of the invention is to improve the speed of operation and the positive control of pneumatically operated fastener driving devices.

It is an additional object of the invention to simplify and improve the construction and assembly of pneuing, and rugged trouble free service.

Other objects, features and advantages of the present invention will be readily apparent from the following detailed description of certain preferred embodiments thereof taken in conjunction with the accompanying drawings, in which:

FIGURE 1 is a side elevational view of a pneumatic fastener driving machine unit constructed and arranged to be mounted upon a suitable fastener carrying or magazine body member or assembly;

FiGURE 2 is a top plan view of the unit shown in FIGURE 1;

FIGURE 3 is a front end elevational view of the pneuiatic unit;

FIGURE 4 is a fragmental, enlarged vertical longi tudinal sectional view through the unit shown in FIG- URES 1 to 3, taken substantially along the section line IV-lV of FIGURE 2 and showing the unit mounted upon a fastener carrying body assembly which is more or less schematically illustrated partly in elevation and partly in section; and

FIGURE 5 is a fragmentary vertical sectional view taken substantially in the same plane as FIGURE 4 but showing only the front end or head portion of the pneumatic unit with the driver and the pneumatic control mechanism illustrated in relative positions assumed during a driving stroke.

In a practical embodiment of the invention a pneumatic driver unit 15 (FIGS. 1, 2 and 3) is constructed and arranged to be mounted upon a body assembly 17 (FIG. 4). As a principal component, the driver unit 15 includes a casing structure which is preferably constructed as a casting of a suitable light weight material such as a suitable aluminum alloy. Such casing comprises an elongated hollow handle portion 18 extending rearwardly from a vertically and laterally enlarged hollow head end portion 19. At its upper end the head portion 19 is open but is operatively closed by a crown closure 20. At its lower end the head portion 19 is provided with a depending boss 21 about a lower opening and to which boss is attached a lower closure member 22 as by means of screws 23.

For attaching the driver unit 15 to the body assembly 17, means such as a pair of spaced depending cars 24 on the rear portion of the handle section 18 are adapted to straddle an upwardly directed attachment boss 25 on the body assembly with suitable means such as attachment bolts 27 extending through suitable aligned apertures 28 in the ears and in the boss 25 and thereby removably secure the rear portions of the driver unit and the body assembly together. Attachment of the forward portion of the body assembly 17 to the driver unit may be accomplished as shown by means of a bolt 29 extending through aligned apertures 36) in a pair of spaced rearwardly extending attachment cars 31 projecting rearwardly from the lower closure member 22 and straddling a forward portion of the body member 17 provided with a bolt hole aligned with the ear apertures 30. Thus, by means of the substantially fore and aft yoke-like attachment means described quick assembly or disassembly of the driver unit 15 and the body assembly 17 can be effected, and the driver unit 15 is adaptable to be mounted selectively upon body units or assemblies that are constructed and arranged for supporting and feeding into position for driving any of a variety of fasteners such as pins, nails or staples, the fasteners in FIGURE 4 being shown as pins 32 of the type commonly referred to as sash pins which are supported in suitable multiples such as in stick form within a longitudinal magazine 33 in the body assembly 17 and fed forwardly therein by suitable feed s v.3 or pusher mechanism (not shown) carried by the body assembly.

At the front end of the body assembly 17 under the head portion 19, and more particularly the bottom or base closure member 22 thereon are provided means for presenting each of the fasteners 32 successively in position to be driven by a driving blade 34 operatively associated with the driving unit 15. In the present instance such means comprise a facing plate 35 having a doorway aperture 37 for passage of the fasteners forwardly therethrough into a vertical driveway 3% defined between the plate 35 and a forward nose piece 39. At their upper end portions the facing plate 35 .and the nose piece 39 have respective-rearward and forward portions that abuttingly underlie the lower closure member in the assembly with the upper end of the driveway 38 aligned with a driver passage opening 40 in the closure member so that the lower end driving tip portion of the driver can normally be supported slidably in the guideway 33 immediately above the foremost of the fasteners to be driven.

For conveniently manually carrying and positioning the machine for driving the fasteners 32 from the driveway 38 into members to be fastened the handle portion or section 18 is preferably shaped longitudinally to extend rearwardly obliquely convergently toward the rear end portion of the body member 17 from the head portion 19 for a suitable length or distance to overlie a hand hole body depression 40, with the remainder of the handle portion extending generally rearwardly and providing a palm depression 4-1 at the juncture of the oblique and terminal rear portion of the handle. The construction and arrangement are such that the forward portion of the handle section 18 can be conveniently held with the fingers of the manipulating hand underneath the handle and the palm above with the thumb projecting forwardly over a control valve assembly 42 mounted at juncture of the upper portion of the front end of the handle with the head 19 between a pair of laterally spaced upwardly and rearwardly projecting guard cars 43. The cars 43 project sufficiently beyond a depressible valve head or button 44 to avoid actuation thereof accidently but requiring that the operators finger or thumb be moved into engagement therewith between the guard ears or ribs 43.

According to the present invention, depressing of the valve button or head 44, results in instantaneous smooth recoiless pneumatic driving of the driving blade 34. This is accomplished by operating the valve assembly 42 to bleed air or other pressure fluid under pressure from a chamber 45 in the upper end portion of the head 19 to cause a control valve piston 47 to be driven (FIG. from a top closure seat 48 on which it normally engages (FIG. 4) at the end or upper lip extremity of a cylinder barrel or boss 49 that projects upwardly within a surrounding pressure fluid chamber or reservoir 5t} inside the head 19. This permits fluid under pressure to spill or expand (see directional arrows, FIG. 5) instantaneously from the chamber 50 over the exposed end seat 48 onto the top of a driving piston 51 to which the upper end portion of the driving blade 34 is attached, thus depressing the driving piston against the action of biasing means such as a spring 52 to actuate the driving blade in a driving stroke.

Since the pressure fluid about the seat lip 48 in the reservoir 5% is already under full pressure head and is of large volume, including not only the immediately surrounding area in the reservoir chamber 59, but also a large unrestricted throat area 53 leading into and connect ing unrestrictedly a large supplementary reserovir chamber 54 throughout substantially the length of the handle section 18, driving of the piston 51 occurs with uni-directional thrust of the air expanding into the cylinder onto the head of the piston 51. There is no recoil because instead of an explosive build-up of energy in the area over the piston head there is, on sudden complete exposure of the piston head to the fluid pressure, actually 4 only escape of fluid from a static volume to which the cylinder head is exposed. Therefore, all of the dynamic pressure thrust is toward the drive piston 51 and not in an upward or rebound direction.

To the attainment of these desirable results, the control valve 42 is a normally closed bleeder valve having attached to the button head 44 a stem 55 carrying a taper faced, O-ring seal valve assembly 57 at the opposite or inner end from the head 44 and normally urged into closing sealing relation against a complementally tapered valve seat 58 at the inner end portion of a valve sleeve bushing 59 housing a valve biasing compression spring 6% Normally the valve 57 is held on its seat 58 by the biasing spring at and fluid pressure, as shown in FIG- URE 4. For opening the valve, pressure applied to the valve head 44 overcomes the biasing spring 60 and un seats the valve 57 as shown in FIGURE 5, thereby opening a passage through the sleeve bushing 59 and vent openings 61 therefrom.

Herein the valve bushing 59 is threaded into the outer end portion of a rearwardly and upwardly oblique blind end bore 62 in the driver unit casing. The inner end portion of this bore communicates by way of a duct '63 with the upper portion of the control piston chamber 45. Thus, when the valve 57 is opened, the control piston chamber 45 is opened to atmosphere and any fluid pressure therein Will bleed oif.

When the valve 57 is closed, fluid under pressure from the chamber 50 forwardly from the throat area 53 bleeds through a passage from the reservoir to supply compressed fluid for operating the valve piston 47. Herein this comprises a continuously open restricted metering orifice 64 and a bore duct as that intersects the bore duct 63 for delivery of the pressure fluid through the port provided by the duct 63 into the control piston chamber 45. Pressure thus created in the chamber 45 acts on the substantial marginal area on the side of the control valve piston which faces toward the closure 2t) and tends to hold the control piston 47 in closing relation upon the driving piston cylinder head seat 48. At its upper end the bore duct 65 is effectively seal d by a gasket 67 clamped against the top of the head 19 by the closure member 20 which is held removably in place by means such as screws 68.

The relative proportions in cross-sectional flow area of the restricted metering orifice 64 and the substantially larger diameter bleed-off duct 63 are such that although in the closed condition of the control valve 57 ample biasing fluid pressure is supplied through the orifice 64 to the control piston chamber 45, in the open, bleed-01f condition of the valve 57 virtually instantaneous pressure drop is attained in the chamber 45 and the pressure drop across the orifice 64 is sufiicient to avoid any appreciable loss of pressure from the pressure chamber 58 that surrounds the cylinder &9.

In order to assure positive action of the control piston d7 responsive to fluid pressure in both directions, it is preferably of substantial diameter and effective area on both sides. To this end the piston 47 is constructed of a diameter substantially larger than the external diameter of the cylinder 49 immediately adjacent to the valve seat 455, and an internal cylindrical surface 69 in the upper end portion of the head 19 is provided concentric with the cylinder 49 for cooperation with the annular periphery of the piston 47. By preference, :1 fluid seal is provided in such annular periphery as by means of an O-ring 76*. Since the range of reciprocal movement of the control piston 47 may be fairly short it will be appreciated that only moderate head room need be provided above the control piston valve seat 48. In such short head room the control piston chamber 45 is of small volume so that bleed-off is accomplished with great speed in the operation of the device. Moreover, the over-all height of the head section of the machine can thus be maintained at a minimum.

In view of the short working stroke of the control piston valve member 47 it is preferably mechanically biased normally toward its seat 48. Herein this is accomplished by means of a coiled compression spring 71 thrusting under compression against the upper face of the piston and against the opposing surface of the closure member 29. The compression loading .of the biasing spring 71 is, of course, substantially less than the force exerted by pres sure fluid in the chamber 5'0 upon the inner or lower dynamic pressure surface of the piston valve 47 exposed to the main pressure chamber 5%.

In order to limit unseating or blow-off, or back-off movement of the piston valve 4-7 depending limit stop means such as an annular flange 72 may be provided on the inner face of the closure member 20; with the biasing spring 72 accommodated Within a central recess 73 encircled by the stop flange. Entrapment of fluid in the recess 73 is avoided by a transverse relief port 74 in the stop flange 72, preferably substantially aligned with the port opening into the bleed-off bore 63. To limit contact, and thus minimize possibility of sticking of the piston valve 47 to the flange 72, a limited area contact shoulder 75 is provided on the upper face of the piston valve.

In order to assure an effective seal between the control piston valve member 47 and the seat 48 to avoid leakage of air into the cylinder 49 in the non-operating condition of the machine, a flexible, resilient valve disk 77 is mounted on the lower side of the piston valve. This valve disk is of such resilient deflectability as to assure thorough sealing conformity to the valve seat 48 under the combined biasing spring and air pressure working against the piston valve in its seated position during non-operating periods.

In order to enable ready replacement of the resilient valve disk 77, it is attached to the piston 47 at an inner margin with the side or face thereof opposite the valve seat-engaging face in loose abutment to the valve piston member. Hence, the valve disk 77 is in the form of an annulus with an inner margin that extends substantially inwardly beyond the inner edge defining the valve seat 48 and is clamped to the piston member 47 by a flange 7 8 on a central sleeve or bushing member 79 threadedly secured into a central bore 80 within the piston 47. However, the sealing valve disk 77 is of a diameter not only to effect full sealing engagement over the entire width of the seat 4-3 but also to extend marginally beyond the outer side of the seat to afford exposure to the pressure of fluid in the chamber 59. This assures that the valve disk 77 will back away from and provide a substantial, uniform air gap between the valve seat 48 and the piston valve for release of fluid into the cylinder and thus as nearly as practicable instantaneous full acceleration of the driving piston 51 for uniform pushing thrust of the driving blade 34 to- Ward and against the head of the fastener 32 to be driven.

It will be observed in FIGURES 4 and 5 that the flange 73 is of smaller diameter than the inside diameter about the valve seat 48 so as to be received freely therein, while the valve disk 77 projects laterally substantially beyond the outer side of the valve seat. As a result, during backing off movement of the piston 47 the resilient valve disk 77 under the influence of fluid pressuer initially on its outer margin and thereafter fully on its exposed face assures lack of any initial drag in opening movement away from the seat 48 but instantaneous large entry opening into the cylinder 49 as the piston valve snaps open toward the stop flange 72.

For guiding reciprocal movements of the piston valve 47 a guide stem 81 is carried rigidly by the closure member 20 concentrically with the piston 47 and is slidably embraced by the sleeve bushing member 79. In addition, the guide stem 81 serves as a piston displacement vent above the drive piston 51. To this end, the lower or inner end portion of the stern has a short blind end bore 82 that communicates by way of a plurality of lateral ports 83 with an annular channel 84 in the inner periphery of the sleeve bushing 79 and which is in communication with the ports 33 in the seated position of the valve piston but is shifted out of communication with the ports 83 in the unseated position of the piston valve as shown in FIG- URE 5. Venting communication from the groove or channel 84 is through a series of lateral ports 85 spaced above the ports 83 and communicating with the inner end portion of an upper blind end bore 87 Within the stem 31 opening from the top thereof to atmosphere above the closure member 20. Through this arrangement, when the piston valve 47 is seated upon the cylinder a vent passage to atmosphere is opened for exhausting pressure fluid above the drive piston 51 incident to its return from a driving stroke. Yet, when the piston valve 4-7 is unseated the vent is immediately closed off to prevent escape of pressure fluid from within the unit. It will be observed that appropriate seals such as O-ring seals are provided at appropriate interface areas of the stem 81 and the bushing sleeve 7 9.

Since for smooth and substantially frictionless operation of the moving parts, it is desirable to entrain in the compressed fluid supplied to the machine a small amount of lubricant, guard means in the form of a baflle cap 88 are preferably provided to overlie the exhaust port at the upper end of the vent bore 87 to prevent spraying of the oil up into the air incident to the rushing exhaust of fluid from the vent. The cap 88 may be secured in place by means of screws 89, with a downturned annular marginal flange '90 of the guard cap seated on spacer lugs or projections 91 on the top of the closure member 20.

Normally the drive piston 51 is held by the biasing spring 52 against an annular inwardly facing shoulder 92 located as closely as practicable to the oppositely, up wardly facing seat 48. Since provision of the stop shoulder 92 provides an annular overhanging portion about the seat 48, a compensating annular upper outer marginal groove 93 is provided adjacent the outer side of the seat 48 in order to maintain the seat at a minimum width to avoid frictional or drag losses in movement of compressed fluid over the seat upon unsea-ting of the piston valve 47.

A desirable relationship between the periphery of the driving piston 51 and the surrounding cylinder Wall comprises a free clearance relationship and with sealing means such as an O-ring 94 operatively seated in the piston periphery.

To provide a return spring centering and bucklepreventing guide, the drive piston 51 is provided with a central smaller diameter depending boss 95 about which the upper end portion of the spring is disposed. This boss 95 also provides means for connecting the driving blade 34 to the piston. For this purpose, the upper end portion of the blade 34 extends upwardly into a downwardly opening slot 97 in the boss. For removably con nectrng the driving blade to the driving plunger or piston 51, retaining means may be provided in the form of pin means such as an elongated key member 98 extending through a transverse bore 99 in the boss 95' and through a matching aperture in the head end portion of the blade 34.

In order to limit the driving stroke of the driving blade 34- to the desired extent, stop means are provided in the lower portion of the cylinder. In the present instance the stop means combine the function of vibration damper and return spring holder. To this end agenerally cupshaped member is provided having a central aperture 101 for passage of the driving blade 34 and providing an annular inturned flange 1%2 upon which the lower end of the return spring 52 thrusts. At its upper end the member 10 1 is provided with a lateral annular flange 163 which in assembly rests upon an annular resilient cushioning or vibration damping member 164 which in turn rests against the upper face of the lower closure member 22, while the lower end portion of the member 101 extends down into a clearance recess 165 affording limited floating movement of the spring retainer and s aman bumper member 100 resting upon the cushioning ring 104.

The upper edge of the stop member flange 193 opposes the lower side of the margin of the drive piston 51 and is engageable by a resilient annular bumper ring 107 of preferably a resiliently flexible or elastic material such as rubber or other elastomeric material carried by the piston. In the present instance a convenient retainer for the resilient bumper 107 comprises a generally channelshaped radially outwardly opening ring member 168 within which the bumper 107 is seated and having the lower flange of the channel substantially narrower than the width of the bumper 107 so as to expose a substantial annular lower outer marginal portion of the bumper ring for engagement with the stop flange 103. For retaining the retainer ring 198 in place on the underside of the piston 51, an upper inner marginal radially inwardly projecting annular seat flange 1119 is provided thereon engaged by the upper end of the return spring 52 which thereby constantly thrusts the retainer ring 1038 against the piston. Through this arrangement, at the end of the driving stroke of the piston 51, as shown in FIGURE 5, the bumper 107 impacts against the stop flange 103 and cushions the stopping of the piston in conjunction with the shock absorbing and cushioning ring 104, the lower side of the ring channel being accommodated within a flaring mouth 11% within the inner side of the flange 103, such mouth being beveled or chamfered to ease the return spring 52 into the recess provided by the retainer and stop member 100 during compression of the spring. It will also be observed in FlG- URE that in the drive stroke limit position of the piston 51, the depending spring guide boss 95 cooperates with the cylindrical wall of the retainer 105) to hold the coils of the spring against undue lateral displacement, which is a desirable relationship to maintain highest efliciency in the spring.

To provide for free breathing within the cylinder 49 under the piston 51 vents are provided herein comprising a plurality of vent ports 111 which may conveniently open into the lower end portion of the cylinder through the front wall of the head 19 (FIGS. 3, 4 and 5). Where, as herein, the stop flange 103' projects upwardly protectively past the vent ports 111, an annular communication channel 112 in the outer periphery of the flange 103- has ports 113 through the flange leading from the interior of the retainer 100 within the cylinder. In addition, vent ports 114 preferably lead from the lower end of the cavity 105 to the outside of the lower closure member 22.

Provisions are made for connecting the reservoir 50, 53, 54 within the unit with a suitable source of pressure fluid. To this end, the rear extremity of the handle 18 is preferably provided with a threaded inlet port 115. Into this inlet port is secured an internally threaded hose nipple receiving member 117 provided with a safety inlet orifice 118. While the orifice 118 will normally allow pressure fluid to maintain the reservoir filled, this orifice assures a suflicient pressure drop upon or restriction upon initial inrush of fluid when the machine is first quick-connected to the fluid source to prevent premature firing of the drive piston. That is, in view of thesmall size of the valve piston hold down bleed orifice 64 there would be a tendency of the valve piston 47 to be blown from its seat in the initial inrush of pressure fluid air into the reservoir. Therefore, by restricting such inrush through the inlet orifice 118 there will be a sufficient restraint or drag or throttling upon initial filling of the reservoir with pressure fluid to enable the piston valve holding pressure bleed through the orifice 64. After the initial filling of the reservoir, of course, a substantially pressure filled condition is maintained therein as long as connection to the pressure source is maintained and therefore the premature firing problem d is only encountered at the initial introduction of pressure fluid into the reservoir.

Where attachment 'of the machine to a fluid supply hose at one side of the head 19 is preferred or more expedient, the inlet orifice may be plugged and the hose attached to a side boss 119 (FIGURE 2) providing an inlet 121) (FIGURE 4) from which leads a restricter orifice 121 bored into the wall of the reservoir and of preferably the same crosssectional flow area as the restricter orifice 118.

From the foregoing it will be apparent that in the use of the fastener driving machine, it is manipulated by the handle 18 into working position and then under full working pressure head or potential energy within the large reservoir within the casing of the unit 15, simple pressing of the valve head 44 results in the substantially instantaneous blowing off of the piston valve 47 and fluid pressure thrusting of the driving piston 51 in a driving stroke. The most efficient reservoir pressure head for any given ize of machine or fastener to be driven may be readily determined. For certain heavier types of fasteners available line pressures up to p.s.i. have been used. As long as the valve 57 is held open the control valve piston 47 will remain unseated due to the differential in pressure thus maintained. Promptly upon closing of the valve 57, pressure bleed through the metering orifice 64 suppleents the piston return spring '71 to return the piston valve 47 to its seat 48, thus closing the piston off from the pressure within the reservoir and at the same time venting the cylinder above the piston to atmosphere through the stem 81, whereupon the drive piston 51 snaps back against the stop shoulder 92. In addition, due to the substantial area on the underside of the valve piston 17 thus relieved of pressure and vented to atmosphere and opposed by pressure within the head chamber 45, a strongly unbalanced pressure relationship is maintained assuring that the valve piston 47 will during non-operating but pressure filled condition of the unit be pressed strongly against the valve seat 48 so as to avoid leakage of pressure fluid into the drive piston cylinder.

Since there is always a large reserve volume of pressure fluid within the reservoir about the cylinder 49, the comparatively small volume of air that spills over into the cylinder 49 incident to driving of the drive piston 51 has virtually no pressure dropping or dissipating eifect. This is especially true because the reservoir is in continuous, open replenishing communication with the pressure fluid source. In practice it is desirable to provide up to ten times the volume of compressed air within the reservoir as compared to the total volume spent on each driving of the drive piston 51, that is, the volumetric displacement above the piston 51 within the cylinder 49 at the end of the driving stroke as depicted in FIGURE 5, depending on the power required.

In view of the immediate full pressure thrust upon the driving piston 51 at the instant of opening the top of the cylinder 49, the volumetric displacement of pressure fluid required to drive the piston with high velocity thrust can be maintained at a minimum. it is, therefore, practical to operate the machine of the present invention with substantially less pressure fluid than has been heretofore possible in fastener driving machines wherein line drag, which is entirely absent in the instant system, has required a wasteful use of fluid in order to attain the desired velocities and power.

It may be pointed out, that while ideally the valve seat lip 48 on the cylinder 49 is preferably exposed uniformly about its entire perimeter to surrounding fluid pressure Within the reservoir, the advantageous operation and results may nevertheless be attained when only a part of the lip may be exposed to the reservoir due to limitations in design in certain cases. For example, one-half to two thirds of the lip may be thus exposed while the remainder may be exposed only after the piston valve has been displaced, and yet attain desirable operating results.

It will be understood that modifications and variations may be effected without departing from the scope of the novel concepts of the present invention.

I claim as my invention:

1. In a pneumatic driving machine, a head portion, a handle portion projecting rearwardly from the head portion, said head portion having therein a compressed fluid reservoir and a cylinder provided with an end opening arranged for exposure within the reservoir, a driving member actuating piston reciprocably operable in said cylinder, a driving member carried by said piston, means normally urging the piston toward said cylinder end, and means normally closing said cylinder end but shiftable toward open position for opening the cylinder to full air pressure within the reservoir for driving the piston and said member in a driving stroke thereof, said cylinder closing means including a pneumatically operated valve piston and means for controlling the operations of said valve piston including a passage from said reservoir to supply compressed fluid from the reservoir for operating said valve piston.

2. In a pneumatic driving unit, a head structure having a reservoir chamber therein, a cylinder having an end opening into said reservoir chamber for exposure of the cylinder thereby to fluid pressure within the reservoir, a piston reciprocably operable in said cylinder responsive to fluid pressure from the reservoir, a reciprocable piston valve for normally closing said open end of the cylinder from the reservoir, means for actuating said piston valve toward open and closed positions, a guide stem for said piston valve with one end of the stem normally exposed to the open end portion of the cylinder andthe opposite end of the stem exposed to atmosphere, and vent passage means including said stem for venting the cylinder to atmosphere in the closed condition of the cylinder 3. In a pneumatic driving machine, a housing including a chambered head portion having an upper end closure, said head portion having therein below said closure a chamber providing a pressure fluid reservoir and a cylinder provided with an end opening arranged for exposure within the reservoir and directed toward said closure, a driving member actuating piston reciprocably operable in said cylinder, a driving member actuated by said piston, the piston being biased toward said cylinder end, a valve of a diameter to close said cylinder end but reciprocably shiftable from a closed to an open position and opening of the cylinder to full fluid pressure from the reservoir for driving the piston in a driving member actuating stroke of the piston, and means on said valve and said closure centrally guiding the valve reciprocably and substantially spaced from the perimeter of the valve and affording on the side of the valve which faces toward said closure a substantial annular marginal area exposed to the effects of pressure fluid.

4. In a pneumatic priving machine, a housing including a chambered head portion having an upper end closure, said head portion having therein below said closure a chamber providing a pressure fluid reservoir and a cylinder provided with an end opening arranged for exposure within the reservoir and directed toward said closure, a driving member actuating piston reciprocably operable in said cylinder, a driving member actuated by said piston, the piston being biased toward said cylinder end, a valve of a diameter to close said cylinder end but reciprocably shiftable from a closed to an open position and opening of the cylinder to full fluid pressure from the reservoir for driving the piston in a driving member actuating stroke of the piston, and means on said valve and said closure centrally guiding the valve reciprocably and substantially spaced from the perimeter of the valve and affording on the side of the valve which faces toward said closure a substantial annular marginal area exposed to the effects of pressure fluid, said guiding means having exhaust passage therethrough and communicating through the valve for exhausting fluid from the cylinder on the return stroke of the piston 5. In a pneumatic driving machine, a housing including a chambered head portion having an upper end closure, said head portion having therein below said closure a chamber providing a pressure fluid reservoir and a cylinder member provided with an end opening arranged for exposure within the reservoir and directed toward said closure, a driver actuating piston reciprocably operable in said cylinder, a driver actuated by said piston, the piston being biased toward said cylinder end, a valve member of a diameter to close said cylinder end, a rigid element extending through said valve member and providing an exhaust passage from said cylinder end to said closure for exhausting fluid from the cylinder for return stroke of the piston, one of said members being movable away from the other of said members to open said cylinder end to full fluid pressure from the reservoir for driving the piston in a driver actuating stroke of the piston, said one member having a surface portion thereon arranged to be exposed to pressure fluid to drive said one member toward said other member for closing said cylinder end, said housing having a passageway therein for delivering pressure fluid to said surface portion of said one member, and a valve structure carried by said housing and including a valve controlling said passageway selectively to open said passageway to exhaust pressure fluid from said portion of said one member, said one member also having a surface thereon exposed to pressure fluid in the reservoir to act on said surface to move said one member away from said other member when said passageway is opened to exhaust.

References Cited in the file of this patent UNITED STATES PATENTS 562,518 Ferguson June 23, 1896 1,164,889 Tessmer Dec. 21, 1915 1,594,232 Zimmermann July 27, 1926 1,832,152 Stewart Nov. 17, 1931 2,412,620 Kipp Dec. 17, 1946 2,542,305 Brinen et a1 Feb. 20, 1951 2,548,736 Morberg Apr. 10, 1951 2,593,231 Wandel Apr. 15, 1952 2,671,214 Iuilfs Mar. 9, 1954 2,677,933 Hopkinson May 11, 1954 2,713,165 Campbell July 19, 1955 2,720,864 Smith Oct. 18, 1955 2,729,198 Faccou Ian. 3, 1956 

1. IN A PNEUMATIC DRIVING MACHINE, A HEAD PORTION, A HANDLE PORTION PROJECTING REARWARDLY FROM THE HEAD PORTION, SAID HEAD PORTION HAVING THEREIN A COMPRESSED FLUID RESEVOIR AND A CYLINDER PROVIDED WITH AN END OPENING ARRANGED FOR EXPOSURE WITHIN THE RESERVOIR, A DRIVING MEMBER ACTUATING PISTON RECIPROCABLY OPERABLE IN SAID CYLINDER, A DRIVING MEMBER CARRIED BY SAID PISTON, MEANS NORMALLY URGING THE PISTON TOWARD SAID CYLINDER END, AND MEANS NORMALLY CLOSING SAID CYLINDER END BUT SHIFTABLE TOWARD OPEN POSITION FOR OPENING THE CYLINDER TO FULL AIR PRESSURE WITHIN THE RESERVIOR FOR DRIVING THE PISTON AND SAID MEMBER IN A DRIVING STROKE THEREOF, SAID CYLINDER CLOSING MEANS INCLUDING A PNEUMATICALLY OPERATED VALVE PISTON AND MEANS FOR CONTROLLING THE OPERATIONS OF SAID VALVE PISTON INCLUDING A PASSAGE FROM SAID RESERVOIR TO SUPPLY COMPRESSED FLUID FROM THE RESERVOIR FOR OPERATING SAID VALVE PISTON. 